Project Summary Two-thirds of the world?s populated areas are currently above the threshold set for light pollution. It is clear from decades of research that light is the most important time cue for the regulation of circadian rhythms. Circadian clocks can be reset by external light cues, and light pulses at night can shift the phase of behavioral rhythms and affect circadian gene expression. Growing evidence also suggests that light pollution causes pathology and physiological disruption. However, the molecular mechanisms that cause these downstream disruptions are unknown. We hypothesize that artificial light at night changes behavior, physiology, and the internal clock. By uncovering the mechanisms underlying responses to artificial light, we will be able to measure, predict and ameliorate potential harmful effects of light pollution, especially because the disruptive effects vary depending on the spectral composition light. Merging mechanistic and behavioral approaches is a way forward to uncover the proximate as well as ultimate consequences of artificial light at night. We will use zebra finches, Taeniopygia guttata, which serve as ideal, diurnal model organisms to test the effects of nocturnal lighting with adapted spectra on physiology, gene expression, and performance. We will quantify the effect of two different wide-spectrum light emitting diodes (LEDs) with different color temperatures on Aim 1) behavior and physiology and Aim 2) circadian pacemaker gene expression. Combining expertise in avian physiology and chronobiology, this collaborative work will lead to a mechanistic understanding of whether circadian pathways are affected by light pollution and whether health effects are long-term. The findings will supply concrete evidence for management practices and urban planning at a global scale, and inform policy makers, governments, and agencies making decisions about the use of alternative LEDs for nighttime illumination. Lastly, this proposal will enhance the infrastructure of research and education at the University of Nevada, Reno, introducing biomedical research experiences to underrepresented minority and female undergraduate students.